提取html中的src 路径

 /// <summary>
        /// 替换body中的img src属性 附加上域名
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        protected virtual string ReplaceImg(string str)
        {
            // 定义正则表达式用来匹配 img 标签   
            Regex regImg = new Regex(@"<img[^<>]*?src[s	
]*=[s	
]*[""']?[s	
]*(?<imgUrl>[^s	
""'<>]*)[^<>]*?/?[s	
]*>", RegexOptions.IgnoreCase);

            // 搜索匹配的字符串   
            MatchCollection matches = regImg.Matches(str);
            int i = 0;
            string[] sUrlList = new string[matches.Count];

            // 取得匹配项列表   
            foreach (Match match in matches)
                sUrlList[i++] = match.Groups["imgUrl"].Value;
            //return sUrlList;
            foreach (var item in sUrlList)
            {
                string newStr = _storeContext.CurrentStore.Url + item.Substring(item.IndexOf('/')+1);
                str = str.Replace(item, newStr);
            }
            return str;
        }